Imitations rarely took the form of imitating the sound that the infant made, but more often involved the mother modeling the word that the sound approximated and expanding on it (e.g., if the infant uttered “da-da-da,” the mother would say “Da-da is working. I am ma-ma”).

https://www.theatlantic.com/health/archive/2014/08/pretending-to-understand-what-babies-say-can-make-them-smarter/379324/